Semiconductor device with partially-etched conductive layer recessed within substrate for bonding to semiconductor die

ABSTRACT

A semiconductor device has a substrate with a die attach area. A conductive layer is formed over a surface of the substrate and extending below the surface. An insulating layer is formed over the surface of the substrate outside the die attach area. A portion of the conductive layer is removed within the die attach area to expose sidewalls of the substrate. The remaining portion of the conductive layer is recessed below the surface of the substrate within the die attach area. A semiconductor die has bumps formed over its active surface. The semiconductor die is mounted to the substrate by bonding the bumps to the remaining portion of the first conductive layer recessed below the first surface of the substrate. The sidewalls of the substrate retain the bumps during bonding to the remaining portion of the conductive layer. An encapsulant is deposited between the semiconductor die and substrate.

CLAIM TO DOMESTIC PRIORITY

The present application is a division of U.S. patent application Ser.No. 12/951,399, now U.S. Pat. No. 8,288,202, filed Nov. 22, 2010, whichapplication is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates in general to semiconductor devices and,more particularly, to a semiconductor device and method of forming apartially-etched conductive layer recessed within a substrate forbonding to a semiconductor die.

BACKGROUND OF THE INVENTION

Semiconductor devices are commonly found in modern electronic products.Semiconductor devices vary in the number and density of electricalcomponents. Discrete semiconductor devices generally contain one type ofelectrical component, e.g., light emitting diode (LED), small signaltransistor, resistor, capacitor, inductor, and power metal oxidesemiconductor field effect transistor (MOSFET). Integrated semiconductordevices typically contain hundreds to millions of electrical components.Examples of integrated semiconductor devices include microcontrollers,microprocessors, charged-coupled devices (CCDs), solar cells, anddigital micro-mirror devices (DMDs).

Semiconductor devices perform a wide range of functions such as signalprocessing, high-speed calculations, transmitting and receivingelectromagnetic signals, controlling electronic devices, transformingsunlight to electricity, and creating visual projections for televisiondisplays. Semiconductor devices are found in the fields ofentertainment, communications, power conversion, networks, computers,and consumer products. Semiconductor devices are also found in militaryapplications, aviation, automotive, industrial controllers, and officeequipment.

Semiconductor devices exploit the electrical properties of semiconductormaterials. The atomic structure of semiconductor material allows itselectrical conductivity to be manipulated by the application of anelectric field or base current or through the process of doping. Dopingintroduces impurities into the semiconductor material to manipulate andcontrol the conductivity of the semiconductor device.

A semiconductor device contains active and passive electricalstructures. Active structures, including bipolar and field effecttransistors, control the flow of electrical current. By varying levelsof doping and application of an electric field or base current, thetransistor either promotes or restricts the flow of electrical current.Passive structures, including resistors, capacitors, and inductors,create a relationship between voltage and current necessary to perform avariety of electrical functions. The passive and active structures areelectrically connected to form circuits, which enable the semiconductordevice to perform high-speed calculations and other useful functions.

Semiconductor devices are generally manufactured using two complexmanufacturing processes, i.e., front-end manufacturing, and back-endmanufacturing, each involving potentially hundreds of steps. Front-endmanufacturing involves the formation of a plurality of die on thesurface of a semiconductor wafer. Each die is typically identical andcontains circuits formed by electrically connecting active and passivecomponents. Back-end manufacturing involves singulating individual diefrom the finished wafer and packaging the die to provide structuralsupport and environmental isolation.

One goal of semiconductor manufacturing is to produce smallersemiconductor devices. Smaller devices typically consume less power,have higher performance, and can be produced more efficiently. Inaddition, smaller semiconductor devices have a smaller footprint, whichis desirable for smaller end products. A smaller die size may beachieved by improvements in the front-end process resulting in die withsmaller, higher density active and passive components. Back-endprocesses may result in semiconductor device packages with a smallerfootprint by improvements in electrical interconnection and packagingmaterials.

In many semiconductor devices, a semiconductor die is mounted tointerconnect sites on a substrate by reflowing bumps to form ametallurgical and electrical interconnect. A solder resist layer istypically formed over the interconnect sites on the substrate withsolder registration opening (SRO) to contain bump material duringreflow. The SRO tends to limit efforts in reducing the bump pitch andincreasing input/output (I/O) count for a semiconductor die.

SUMMARY OF THE INVENTION

A need exists to reduce bump pitch and increase I/O count for asemiconductor die. Accordingly, in one embodiment, the present inventionis semiconductor device comprising a substrate including a die attacharea. A first conductive layer is recessed below a first surface of thesubstrate within the die attach area to expose sidewalls of thesubstrate. A semiconductor die includes a plurality of bumps formed overthe semiconductor die. The semiconductor die is disposed within the dieattach area with the bumps bonded to the first conductive layer andcontacting the sidewalls of the substrate.

In another embodiment, the present invention is a semiconductor devicecomprising a substrate including a die attach area. A first conductivelayer is recessed below a first surface of the substrate within the dieattach area to expose sidewalls of the substrate. A semiconductor die isdisposed over the die attach area. A plurality of bumps is disposedbetween the semiconductor die and the first conductive layer within thedie attach area.

In another embodiment, the present invention is a semiconductor devicecomprising a substrate and first conductive layer recessed below a firstsurface of the substrate to expose sidewalls of the substrate.

In another embodiment, the present invention is a semiconductor devicecomprising a substrate including a die attach area. A first conductivelayer is recessed below a first surface of the substrate. Asemiconductor die is disposed within the die attach area of thesubstrate and electrically connected to the first conductive layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a PCB with different types of packages mounted to itssurface;

FIGS. 2 a-2 c illustrate further detail of the representativesemiconductor packages mounted to the PCB;

FIGS. 3 a-3 c illustrate a semiconductor wafer with a plurality ofsemiconductor die separated by saw streets;

FIGS. 4 a-4 i illustrate a process of forming a partially-etchedconductive layer recessed within a substrate for bonding to asemiconductor die; and

FIG. 5 illustrates stacked semiconductor die bonded to substrate withpartially-etched recessed conductive layer.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is described in one or more embodiments in thefollowing description with reference to the figures, in which likenumerals represent the same or similar elements. While the invention isdescribed in terms of the best mode for achieving the invention'sobjectives, it will be appreciated by those skilled in the art that itis intended to cover alternatives, modifications, and equivalents as maybe included within the spirit and scope of the invention as defined bythe appended claims and their equivalents as supported by the followingdisclosure and drawings.

Semiconductor devices are generally manufactured using two complexmanufacturing processes: front-end manufacturing and back-endmanufacturing. Front-end manufacturing involves the formation of aplurality of die on the surface of a semiconductor wafer. Each die onthe wafer contains active and passive electrical components, which areelectrically connected to form functional electrical circuits. Activeelectrical components, such as transistors and diodes, have the abilityto control the flow of electrical current. Passive electricalcomponents, such as capacitors, inductors, resistors, and transformers,create a relationship between voltage and current necessary to performelectrical circuit functions.

Passive and active components are formed over the surface of thesemiconductor wafer by a series of process steps including doping,deposition, photolithography, etching, and planarization. Dopingintroduces impurities into the semiconductor material by techniques suchas ion implantation or thermal diffusion. The doping process modifiesthe electrical conductivity of semiconductor material in active devices,transforming the semiconductor material into an insulator, conductor, ordynamically changing the semiconductor material conductivity in responseto an electric field or base current. Transistors contain regions ofvarying types and degrees of doping arranged as necessary to enable thetransistor to promote or restrict the flow of electrical current uponthe application of the electric field or base current.

Active and passive components are formed by layers of materials withdifferent electrical properties. The layers can be formed by a varietyof deposition techniques determined in part by the type of materialbeing deposited. For example, thin film deposition may involve chemicalvapor deposition (CVD), physical vapor deposition (PVD), electrolyticplating, and electroless plating processes. Each layer is generallypatterned to form portions of active components, passive components, orelectrical connections between components.

The layers can be patterned using photolithography, which involves thedeposition of light sensitive material, e.g., photoresist, over thelayer to be patterned. A pattern is transferred from a photomask to thephotoresist using light. The portion of the photoresist patternsubjected to light is removed using a solvent, exposing portions of theunderlying layer to be patterned. The remainder of the photoresist isremoved, leaving behind a patterned layer. Alternatively, some types ofmaterials are patterned by directly depositing the material into theareas or voids formed by a previous deposition/etch process usingtechniques such as electroless and electrolytic plating.

Depositing a thin film of material over an existing pattern canexaggerate the underlying pattern and create a non-uniformly flatsurface. A uniformly flat surface is required to produce smaller andmore densely packed active and passive components. Planarization can beused to remove material from the surface of the wafer and produce auniformly flat surface. Planarization involves polishing the surface ofthe wafer with a polishing pad. An abrasive material and corrosivechemical are added to the surface of the wafer during polishing. Thecombined mechanical action of the abrasive and corrosive action of thechemical removes any irregular topography, resulting in a uniformly flatsurface.

Back-end manufacturing refers to cutting or singulating the finishedwafer into the individual die and then packaging the die for structuralsupport and environmental isolation. To singulate the die, the wafer isscored and broken along non-functional regions of the wafer called sawstreets or scribes. The wafer is singulated using a laser cutting toolor saw blade. After singulation, the individual die are mounted to apackage substrate that includes pins or contact pads for interconnectionwith other system components. Contact pads formed over the semiconductordie are then connected to contact pads within the package. Theelectrical connections can be made with solder bumps, stud bumps,conductive paste, or wirebonds. An encapsulant or other molding materialis deposited over the package to provide physical support and electricalisolation. The finished package is then inserted into an electricalsystem and the functionality of the semiconductor device is madeavailable to the other system components.

FIG. 1 illustrates electronic device 50 having a chip carrier substrateor printed circuit board (PCB) 52 with a plurality of semiconductorpackages mounted on its surface. Electronic device 50 may have one typeof semiconductor package, or multiple types of semiconductor packages,depending on the application. The different types of semiconductorpackages are shown in FIG. 1 for purposes of illustration.

Electronic device 50 may be a stand-alone system that uses thesemiconductor packages to perform one or more electrical functions.Alternatively, electronic device 50 may be a subcomponent of a largersystem. For example, electronic device 50 may be part of a cellularphone, personal digital assistant (PDA), digital video camera (DVC), orother electronic communication device. Alternatively, electronic device50 can be a graphics card, network interface card, or other signalprocessing card that can be inserted into a computer. The semiconductorpackage can include microprocessors, memories, application specificintegrated circuits (ASIC), logic circuits, analog circuits, RFcircuits, discrete devices, or other semiconductor die or electricalcomponents. The miniaturization and the weight reduction are essentialfor these products to be accepted by the market. The distance betweensemiconductor devices must be decreased to achieve higher density.

In FIG. 1, PCB 52 provides a general substrate for structural supportand electrical interconnect of the semiconductor packages mounted on thePCB. Conductive signal traces 54 are formed over a surface or withinlayers of PCB 52 using evaporation, electrolytic plating, electrolessplating, screen printing, or other suitable metal deposition process.Signal traces 54 provide for electrical communication between each ofthe semiconductor packages, mounted components, and other externalsystem components. Traces 54 also provide power and ground connectionsto each of the semiconductor packages.

In some embodiments, a semiconductor device has two packaging levels.First level packaging is a technique for mechanically and electricallyattaching the semiconductor die to an intermediate carrier. Second levelpackaging involves mechanically and electrically attaching theintermediate carrier to the PCB. In other embodiments, a semiconductordevice may only have the first level packaging where the die ismechanically and electrically mounted directly to the PCB.

For the purpose of illustration, several types of first level packaging,including wire bond package 56 and flip chip 58, are shown on PCB 52.Additionally, several types of second level packaging, including ballgrid array (BGA) 60, bump chip carrier (BCC) 62, dual in-line package(DIP) 64, land grid array (LGA) 66, multi-chip module (MCM) 68, quadflat non-leaded package (QFN) 70, and quad flat package 72, are shownmounted on PCB 52. Depending upon the system requirements, anycombination of semiconductor packages, configured with any combinationof first and second level packaging styles, as well as other electroniccomponents, can be connected to PCB 52. In some embodiments, electronicdevice 50 includes a single attached semiconductor package, while otherembodiments call for multiple interconnected packages. By combining oneor more semiconductor packages over a single substrate, manufacturerscan incorporate pre-made components into electronic devices and systems.Because the semiconductor packages include sophisticated functionality,electronic devices can be manufactured using cheaper components and astreamlined manufacturing process. The resulting devices are less likelyto fail and less expensive to manufacture resulting in a lower cost forconsumers.

FIGS. 2 a-2 c show exemplary semiconductor packages. FIG. 2 aillustrates further detail of DIP 64 mounted on PCB 52. Semiconductordie 74 includes an active region containing analog or digital circuitsimplemented as active devices, passive devices, conductive layers, anddielectric layers formed within the die and are electricallyinterconnected according to the electrical design of the die. Forexample, the circuit may include one or more transistors, diodes,inductors, capacitors, resistors, and other circuit elements formedwithin the active region of semiconductor die 74. Contact pads 76 areone or more layers of conductive material, such as aluminum (Al), copper(Cu), tin (Sn), nickel (Ni), gold (Au), or silver (Ag), and areelectrically connected to the circuit elements formed withinsemiconductor die 74. During assembly of DIP 64, semiconductor die 74 ismounted to an intermediate carrier 78 using a gold-silicon eutecticlayer or adhesive material such as thermal epoxy or epoxy resin. Thepackage body includes an insulative packaging material such as polymeror ceramic. Conductor leads 80 and bond wires 82 provide electricalinterconnect between semiconductor die 74 and PCB 52. Encapsulant 84 isdeposited over the package for environmental protection by preventingmoisture and particles from entering the package and contaminating die74 or bond wires 82.

FIG. 2 b illustrates further detail of BCC 62 mounted on PCB 52.Semiconductor die 88 is mounted over carrier 90 using an underfill orepoxy-resin adhesive material 92. Bond wires 94 provide first levelpackaging interconnect between contact pads 96 and 98. Molding compoundor encapsulant 100 is deposited over semiconductor die 88 and bond wires94 to provide physical support and electrical isolation for the device.Contact pads 102 are formed over a surface of PCB 52 using a suitablemetal deposition process such as electrolytic plating or electrolessplating to prevent oxidation. Contact pads 102 are electricallyconnected to one or more conductive signal traces 54 in PCB 52. Bumps104 are formed between contact pads 98 of BCC 62 and contact pads 102 ofPCB 52.

In FIG. 2 c, semiconductor die 58 is mounted face down to intermediatecarrier 106 with a flip chip style first level packaging. Active region108 of semiconductor die 58 contains analog or digital circuitsimplemented as active devices, passive devices, conductive layers, anddielectric layers formed according to the electrical design of the die.For example, the circuit may include one or more transistors, diodes,inductors, capacitors, resistors, and other circuit elements withinactive region 108. Semiconductor die 58 is electrically and mechanicallyconnected to carrier 106 through bumps 110.

BGA 60 is electrically and mechanically connected to PCB 52 with a BGAstyle second level packaging using bumps 112. Semiconductor die 58 iselectrically connected to conductive signal traces 54 in PCB 52 throughbumps 110, signal lines 114, and bumps 112. A molding compound orencapsulant 116 is deposited over semiconductor die 58 and carrier 106to provide physical support and electrical isolation for the device. Theflip chip semiconductor device provides a short electrical conductionpath from the active devices on semiconductor die 58 to conductiontracks on PCB 52 in order to reduce signal propagation distance, lowercapacitance, and improve overall circuit performance. In anotherembodiment, the semiconductor die 58 can be mechanically andelectrically connected directly to PCB 52 using flip chip style firstlevel packaging without intermediate carrier 106.

FIG. 3 a shows a semiconductor wafer 120 with a base substrate material122, such as silicon, germanium, gallium arsenide, indium phosphide, orsilicon carbide, for structural support. A plurality of semiconductordie or components 124 is formed on wafer 120 separated by saw streets126 as described above.

FIG. 3 b shows a cross-sectional view of a portion of semiconductorwafer 120. Each semiconductor die 124 has a back surface 128 and activesurface 130 containing analog or digital circuits implemented as activedevices, passive devices, conductive layers, and dielectric layersformed within the die and electrically interconnected according to theelectrical design and function of the die. For example, the circuit mayinclude one or more transistors, diodes, and other circuit elementsformed within active surface 130 to implement analog circuits or digitalcircuits, such as digital signal processor (DSP), ASIC, memory, or othersignal processing circuit. Semiconductor die 124 may also containintegrated passive devices (IPDs), such as inductors, capacitors, andresistors, for RF signal processing. In one embodiment, semiconductordie 124 is a flipchip type semiconductor die.

An electrically conductive layer 132 is formed over active surface 130using PVD, CVD, electrolytic plating, electroless plating process, orother suitable metal deposition process. Conductive layer 132 can be oneor more layers of Al, Cu, Sn, Ni, Au, Ag, or other suitable electricallyconductive material. Conductive layer 132 operates as contact padselectrically connected to the circuits on active surface 130.

An electrically conductive bump material is deposited over contact pads132 using an evaporation, electrolytic plating, electroless plating,ball drop, or screen printing process. The bump material can be Al, Sn,Ni, Au, Ag, Pb, Bi, Cu, solder, and combinations thereof, with anoptional flux solution. For example, the bump material can be eutecticSn/Pb, high-lead solder, or lead-free solder. The bump material isbonded to contact pads 132 using a suitable attachment or bondingprocess. In one embodiment, the bump material is reflowed by heating thematerial above its melting point to form spherical balls or bumps 134.In some applications, bumps 134 are reflowed a second time to improveelectrical contact to contact pads 132. The bumps can also becompression bonded to contact pads 132. Bumps 134 represent one type ofinterconnect structure that can be formed over contact pads 132. Theinterconnect structure can also use stud bump, micro bump, conductivepillars, or other electrical interconnect. Bumps 134 are electricallyconnected through contact pads 132 to circuits contained in activesurface 130.

In FIG. 3 c, semiconductor wafer 120 is singulated through saw street126 using a saw blade or laser cutting tool 136 into individualsemiconductor die 124.

FIGS. 4 a-4 i illustrate, in relation to FIGS. 1 and 2 a-2 c, a processof forming a partially-etched conductive layer recessed within asubstrate for bonding to a semiconductor die. In FIG. 4 a, asemiconductor wafer or substrate 140 contains a base material, such assilicon, germanium, gallium arsenide, indium phosphide, or siliconcarbide, for structural support. Substrate 140 can contain embeddedsemiconductor die, semiconductor components, or passive devices.Substrate 140 has surface 142 and opposing surface 144.

In FIG. 4 b, a plurality of vias is formed through substrate 140 usinglaser drilling, mechanical drilling, or deep reactive ion etching(DRIE). The vias are filled with Al, Cu, Sn, Ni, Au, Ag, titanium (Ti),tungsten (W), poly-silicon, or other suitable electrically conductivematerial using electrolytic plating, electroless plating process, orother suitable metal deposition process to form z-direction verticalinterconnect conductive vias 146.

In FIG. 4 c, an electrically conductive layer or RDL 148 is formed oversurface 142 of substrate 140 and conductive vias 146 using a patterningand metal deposition process such as printing, PVD, CVD, sputtering,electrolytic plating, and electroless plating. Conductive layer 148 canbe one or more layers of Al, Cu, Sn, Ni, Au, Ag, or other suitableelectrically conductive material. Conductive layer 148 extends belowsurface 142 with electrical connection to conductive vias 146.Conductive layer 148 is initially made thick, e.g., 6 micrometers (μm),particular in die attach area 150 designated for later mounting ofsemiconductor die 124.

An electrically conductive layer or RDL 152 is formed over surface 144of substrate 140 and conductive vias 146 using a patterning and metaldeposition process such as printing, PVD, CVD, sputtering, electrolyticplating, and electroless plating. Conductive layer 152 can be one ormore layers of Al, Cu, Sn, Ni, Au, Ag, or other suitable electricallyconductive material. Conductive layer 152 is electrically connected toconductive vias 146.

In FIG. 4 d, a solder resist or insulating layer 154 is formed oversurface 142 of substrate 140 and conductive layer 148 using PVD, CVD,printing, spin coating, spray coating, sintering or thermal oxidation.The insulating layer 154 contains one or more layers of silicon dioxide(SiO2), silicon nitride (Si3N4), silicon oxynitride (SiON), tantalumpentoxide (Ta2O5), aluminum oxide (Al2O3), or other material havingsimilar insulating and structural properties. A portion of insulatinglayer 154 is removed by an etching process over die attach area 150 forbonding of semiconductor die 124 to conductive layer 148.

A solder resist or insulating layer 156 is formed over surface 144 ofsubstrate 140 and conductive layer 152 using PVD, CVD, printing, spincoating, spray coating, sintering or thermal oxidation. The insulatinglayer 156 contains one or more layers of SiO2, Si3N4, SiON, Ta2O5,Al2O3, or other material having similar insulating and structuralproperties. A portion of insulating layer 156 is removed by an etchingprocess to expose conductive layer 152.

In FIG. 4 e, an insulating layer 158 is formed over insulating layer 156and conductive layer 152 using PVD, CVD, printing, spin coating, spraycoating, sintering or thermal oxidation. The insulating layer 158contains one or more layers of SiO2, Si3N4, SiON, Ta2O5, Al2O3, or othermaterial having similar insulating and structural properties. In oneembodiment, insulating layer 158 is a dry film layer.

In FIG. 4 f, a portion of conductive layer 148 within die attach area150 is removed a wet etching process (immersion or spray) or dry etchingprocess (physical sputtering, plasma, reactive ion etching). In oneembodiment, the thickness of conductive layer 148 within die attach area150 is reduced by 50 percent or 10-20 μm. The etchant does not reactwith substrate 140 or insulating layer 154. Accordingly, removing aportion of conductive layer 148 leaves a recess in substrate 140 belowsurface 142. The sidewalls of the recessed substrate 140, i.e., betweenthe remaining partially-etched conductive layer 148 and surface 142,constitute a prepreg wall 160. The portion of conductive layer 148outside die attach area 150 remains intact by nature of insulating layer154. Likewise, insulating layer 158 protects conductive layer 152 fromthe etching process.

In FIG. 4 g, semiconductor die 124 from FIGS. 3 a-3 c are positionedover and mounted to substrate 140 using a pick and place operation. Thepartially-etched conductive layer 148 is substantially the same width orslightly wider than bumps 134. Bumps 134 are metallurgically andelectrically connected to the partially-etched conductive layer 148 byreflow and pressure. A force can be applied to back surface 128 ofsemiconductor die 124 to assist with the bump bonding. The recessedsubstrate 140 aids with alignment of bumps 134 to conductive layer 148.

FIG. 4 h shows semiconductor die 124 mounted to substrate 140. Bumps 134reside partially within the recessed substrate 140 and contact thepartially-etched conductive layer 148, as well as prepreg walls 160. Bydisposing bumps 134 partially within the recessed substrate, thecombined height of semiconductor die 124 and substrate 140 is reduced.The roughness of substrate 140 strengths the bond between semiconductordie 124 and the substrate. The recessed substrate 140 with prepreg walls160 is well suited for fine bump pitch and high I/O count semiconductordie. Prepreg walls 160 act as a mask or barrier to restrain outward flowof bump material during reflow to reduce occurrences of bump bridging orelectrical shorting between adjacent structures.

In high routing density applications, it is desirable to minimize escapepitch of conductive layer 148. The escape pitch between conductive layer148 can be reduced by eliminating the masking layer for the purpose ofreflow containment, i.e., by reflowing the bump material without amasking layer. Since no solder registration opening (SRO) is formedaround conductive layer 148, the conductive layer can be formed with afiner pitch, i.e., the conductive layer 148 can be disposed closertogether or to nearby structures. When the bump material is reflowedwithout a masking layer to metallurgically and electrically connectcontact pad 132 to conductive layer 148, the wetting and surface tensioncauses the bump material to maintain self-confinement and be retainedwithin the space between the contact pad and conductive layer andportion of substrate 140 immediately adjacent to conductive layer 148substantially within the footprint of the contact pads.

To achieve the desired self-confinement property, the bump material canbe immersed in a flux solution prior to placement on conductive layer148 to selectively render the region contacted by the bump material morewettable than the surrounding area of the conductive layer. The moltenbump material remains confined substantially within the area defined bythe contact pad due to the wettable properties of the flux solution. Thebump material does not run-out to the less wettable areas. A thin oxidelayer or other insulating layer can be formed over areas where bumpmaterial is not intended to make the area less wettable. Hence, maskinglayer 154 is not needed around contact pad 132 or conductive layer 148.

An encapsulant or molding compound 164 is deposited betweensemiconductor die 124 and substrate 140 using a mold underfill (MUF)process. The encapsulant is injected under pressure from a dispensingneedle through the gap under semiconductor die 124 and substrate 140around bumps 134. A vacuum assist can draw encapsulant 164 to aid withuniform distribution. Encapsulant 164 can be polymer composite material,such as epoxy resin with filler, epoxy acrylate with filler, or polymerwith proper filler. Encapsulant 164 is non-conductive andenvironmentally protects the semiconductor device from external elementsand contaminants.

In FIG. 4 i, insulating layer 158 is removed by chemical etching or wetstripping to expose conductive layer 152. An electrically conductivebump material is deposited over the exposed portion of conductive layer152 using an evaporation, electrolytic plating, electroless plating,ball drop, or screen printing process. The bump material can be Al, Sn,Ni, Au, Ag, Pb, Bi, Cu, solder, and combinations thereof, with anoptional flux solution. For example, the bump material can be eutecticSn/Pb, high-lead solder, or lead-free solder. The bump material isbonded to conductive layer 152 using a suitable attachment or bondingprocess. In one embodiment, the bump material is reflowed by heating thematerial above its melting point to form spherical balls or bumps 166.In some applications, bumps 166 are reflowed a second time to improveelectrical contact to conductive layer 152. An under bump metallization(UBM) can be formed under bumps 166. The bumps can also be compressionbonded to conductive layer 152. Bumps 166 represent one type ofinterconnect structure that can be formed over conductive layer 152. Theinterconnect structure can also use stud bump, micro bump, or otherelectrical interconnect.

FIG. 5 shows two stacked semiconductor devices 170, each includingsemiconductor die 124 and substrate 140. Semiconductor die 124 areelectrically connected through bumps 134 and substrate 140. Bumps 134reside partially within the recessed substrate 140 and contact thepartially-etched conductive layer 148, as well as prepreg walls 160. Bydisposing bumps 134 partially within the recessed substrate, thecombined height of semiconductor die 124 and substrate 140 is reduced.The roughness of substrate 140 strengths the bond between semiconductordie 124 and the substrate. The recessed substrate 140 with prepreg walls160 is well suited for fine bump pitch and high I/O count semiconductordie. Prepreg walls 160 act as a mask to restrain outward flow of bumpmaterial during reflow to reduce occurrences of bump bridging orelectrical shorting between adjacent structures.

While one or more embodiments of the present invention have beenillustrated in detail, the skilled artisan will appreciate thatmodifications and adaptations to those embodiments may be made withoutdeparting from the scope of the present invention as set forth in thefollowing claims.

What is claimed:
 1. A semiconductor device, comprising: a substrateincluding a die attach area; a first conductive layer recessed below afirst surface of the substrate within the die attach area to exposesidewalls of the substrate; and a semiconductor die including aplurality of bumps formed over the semiconductor die, the semiconductordie being disposed within the die attach area with the bumps bonded tothe first conductive layer and contacting the sidewalls of thesubstrate.
 2. The semiconductor device of claim 1, wherein the firstconductive layer within the die attach area is recessed 10-20micrometers below the first surface of the substrate.
 3. Thesemiconductor device of claim 1, further including an insulating layerformed over the first surface of the substrate outside the die attacharea.
 4. The semiconductor device of claim 1, further including anunderfill material deposited between the semiconductor die andsubstrate.
 5. The semiconductor device of claim 1, further including: aconductive via formed through the substrate; and a second conductivelayer formed over a second surface of the substrate opposite the firstsurface of the substrate, the second conductive layer being electricallyconnected to the conductive via.
 6. The semiconductor device of claim 5,further including a plurality of stacked semiconductor deviceselectrically connected through the bumps, first conductive layer, secondconductive layer, and conductive via.
 7. A semiconductor device,comprising: a substrate including a die attach area; a first conductivelayer recessed below a first surface of the substrate within the dieattach area to expose sidewalls of the substrate; a semiconductor diedisposed over the die attach area; and a plurality of bumps disposedbetween the semiconductor die and the first conductive layer within thedie attach area.
 8. The semiconductor device of claim 7, wherein thefirst conductive layer within the die attach area is recessed 10-20micrometers below the first surface of the substrate.
 9. Thesemiconductor device of claim 7, further including an insulating layerformed over the first surface of the substrate outside the die attacharea.
 10. The semiconductor device of claim 7, further including anunderfill material deposited between the semiconductor die andsubstrate.
 11. The semiconductor device of claim 7, further including: aconductive via formed through the substrate; and a second conductivelayer formed over a second surface of the substrate opposite the firstsurface of the substrate, the second conductive layer being electricallyconnected to the conductive via.
 12. The semiconductor device of claim11, further including an insulating layer over the second conductivelayer and second surface of the substrate.
 13. The semiconductor deviceof claim 11, further including a plurality of stacked semiconductordevices electrically connected through the bumps, first conductivelayer, second conductive layer, and conductive via.
 14. A semiconductordevice, comprising: a substrate; and a first conductive layer recessedbelow a first surface of the substrate to expose sidewalls of thesubstrate.
 15. The semiconductor device of claim 14, further including asemiconductor die disposed over the substrate and electrically connectedto the first conductive layer.
 16. The semiconductor device of claim 15,further including a plurality of bumps disposed between thesemiconductor die and the first conductive layer.
 17. The semiconductordevice of claim 15, further including an underfill material depositedbetween the semiconductor die and substrate.
 18. The semiconductordevice of claim 14, wherein the first conductive layer is recessed 10-20micrometers below the first surface of the substrate.
 19. Thesemiconductor device of claim 14, further including: a conductive viaformed through the substrate; and a second conductive layer formed overa second surface of the substrate, the second conductive layer beingelectrically connected to the conductive via.
 20. The semiconductordevice of claim 19, further including a plurality of stackedsemiconductor devices electrically connected through the bumps, firstconductive layer, second conductive layers, and conductive via.
 21. Asemiconductor device, comprising: a substrate including a die attacharea; a first conductive layer recessed below a first surface of thesubstrate to expose sidewalls of the substrate; and a semiconductor diedisposed within the die attach area of the substrate.
 22. Thesemiconductor device of claim 21, further including a plurality of bumpsdisposed between the semiconductor die and the first conductive layerwithin the die attach area.
 23. The semiconductor device of claim 21,wherein the first conductive layer within the die attach area isrecessed 10-20 micrometers below the first surface of the substrate. 24.The semiconductor device of claim 21, further including an insulatinglayer formed over the first surface of the substrate outside the dieattach area.
 25. The semiconductor device of claim 21, further includingan underfill material deposited between the semiconductor die andsubstrate.